Control of moving surfaces

ABSTRACT

A control unit for a ship stabilizer fin is arranged to provide a signal indicative of the tilting torque applied to the fin and which is modified by a cam to provide a signal which varies the output of a roll-velocity sensing gyro which controls the fin settings. The change in the center of pressure of the fin which change in angle of attack can thus be compensated for. The invention has utility in the field of small ship stabilizers such as yacht stabilizers.

United States Patent Roger Edward Gwynn Catiord;

Michael John Turnham, Anerley; Alexander Arthur Tann, West Wickharn,

Inventors CONTROL OF MOVING SURFACES Primary Examiner-Andrew l-l. Farrell Attorney-Holman & Stern ABSTRACT: A control unit for a ship stabilizer fin is arranged to provide a signal indicative of the tilting torque applied to the fin and which is modified by a cam to provide a signal 6 Claims 1 Drawing which varies the output of a roll-velocity sensing gyro which US. Cl 114/126 controls the fin settings. The change in the center of pressure Int. Cl B63b 39/06 of the fin which change in angle of attack can thus be compen- Field of Search 1 14/ 1 26, sated for The invention has utility in the field of small ship sta- 122 bilizers such as yacht stabilizers.

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37 a V 3a 2b HYDRAuLu: N PRESSURE 24 9 moR/wuc l f- FRESSURE 4 4| REGULATO CONTROL OF MOVING SURFACES This invention relates to the control of fins which require to have their angles of attack to a fluid stream flowing over the fins altered by tilting. Such fins are used in ship stabilizers. However, the invention may well have wider utility as, for example, in the movement of aircraft control surfaces.

The use of fin stabilizers to minimize rolling movements of ships up to several thousand tons displacement is relatively well known. The fins project from the port and starboard sides of the ship beneath the waterline and their angle of attack to the water is changed by turning movement of a supporting shaft integral with the fin and extending into the vessel. The fin on the port side is tilted in the opposite direction to that on the starboard side to provide, together, a stabilizing moment acting in the opposite direction to the rolling motion of the ship.

The supporting shaft for each fin passes through a gland in the ships hull located beneath the waterline. The inner end of the fin is turned by a suitable motor driven assembly through an angle determined by roll-sensing means mounted elsewhere in the ship. The commencement of a roll is detected by the roll-sensing means and used to alter the tilt angles of the fins so that they exert a moment on the ship which counters the rolling moment.

During operation of the stabilizer, each fin is always acting to generate a hydrodynamic lift which varies with its angle of attack and the speed of the fin through the water. In practice a linear relationship exists between the lift generated by a fin and its angle of attack to the water. However no such linear relationship exists between the torque on the fin and its angle of attack, because the center of pressure of the fin changes.

An object of this invention is the provision of an improved control unit.

in accordance with the broadest aspect of the invention a control unit for supplying a signal to a tilting mechanism of a fin providing control surfaces in a fluid medium, includes a member providing a first signal to be corrected by appropriate tilting of the fin, a device providing a second signal representative of the torque applied to tilt the fin, a modifying element having a prearranged nonlinear characteristic and arranged to modify the second signal to provide a third signal, and a computer controlling the operation of the fin-tilting mechanism and computing the required tilt angle from the first and third signals.

ln its broadest aspect the invention is applicable to aircraft control surfaces, such as an aircraft rudder, as well as to marine fin control surfaces such as a stabilizing fin. The expression fin is used loosely to cover any control surface whose angle of attack to an incident fluid stream is to be varied to provide a control of the movement of the body on which the control surface is mounted. The invention is particularly useful in its narrower form, outlined below, to the positioning of a ship-stabilizing fin as described in our copending U.S. Pat. Application Ser. No. 829,156 filed May 23, I969, and entitled Stabilizers hereby inserted by way of reference.

In accordance with the narrower aspect of the invention a control unit for varying the tilt angle of a ship-stabilizing fin, includes a member for providing a first signal instantaneously representative of the roll velocity of the ship, a tin-tilting mechanism adapted to vary the angle of attack of the fin through the water to stabilize the roll, a device for providing a second signal representative of the torque applied to tilt the fin, a modifying element having a prearranged nonlinear characteristic for modifying the second signal to provide a third signal which takes account of the change in the center of pressure with change in angle of attack of the fin, and a computer controlling operation of the fin-tilting mechanism and determining the fin tilt angle from the first and third signals.

Suitably the member comprises a rate gyro which preferably is arranged to apply its output, which is representative of the rate of roll of the ship, to an amplifier by way of a floating lever. Advantageously the fulcrum of the floating lever is positioned by the third signal so that, the greater the torque applied to the fin, the greater is the displacement of the fulcrum of the floating lever from a rest position which it occupies when the ship is not rolling.

The modifying element is suitably a cam. Where use is made of a floating lever, the cam is suitably arranged to move the fulcrum axis of the lever parallel to itself. The second or torque signal may be derived from the fin or the tilting mechanism. Preferably, however, it is determined from the magnitude of a fluid pressure signal used to determine the tilt of the fin.

Advantageously the fin tilting mechanism is fluid controlled, being either pneumatic or hydraulic, and a suitable pressure regulator whose setting is determined by the computer may be used to supply fluid at an adjustable pressure to the fin-tilting mechanism. When the modifying element is a cam, this is preferably positionally controlled by the setting of the pressure regulator which is, of course, an accurate measure of the torque exerted on the fin when a fluid system is used to control the fin-tilting mechanism.

In some cases the fin may be hydrodynamically balanced, that is to say that the torque applied to the portion of the fin on one side of the tilt axis by the water flowing past it is substantially balanced by a torque applied in the opposite direction by the portion of the fin on the other side of the tilt axis. Obviously, in such an arrangement, the torque required to move the fin is negligible. The invention may nevertheless be used with such an arrangement by incorporating a bias spring tending to restore the fin to its midposition and against which the torque applied to tilt the fin acts.

The invention will now be described in more detail, by way of example only, with reference to the accompanying drawing which shows, diagrammatically, a control unit for varying the tilt angle ofa pair of ship-stabilizing fins.

Referring to the drawing, a ship (not shown) is provided with port and starboard stabilizing fins l, 2. Each fin is tiltablc about an axis of a shaft 3,4 and is provided with a crosshead 5, 6. The free end of one arm of the crosshead 5, 6 is shown connected by a spring 7, 8 to an anchorage 9, 10 from which a fluid-operated piston and cylinder unit ll, 12 extends to a pivot point 13, 14 adjacent the other end of the crosshead 5, 6, In actual practice the springs 7, 8 are unnecessary when the fin is not hydrodynamically balanced and are normally only employed when the fin l, 2 is hydrodynamically balanced. The piston and cylinder units ll, 12 each contain a double-sided piston and two working chambers disposed, respectively, on opposite sides of the piston. The piston and cylinder units together with the crossheads and centering springs, if used, provide the fin-tilting mechanism for respective fins of the stabilizer. For a more comprehensive description of the fin construction and the way it is mounted, reference should be had to our above-mentioned copending application.

Hydraulic circuits 20 interconnect one working chamber of each of the piston and cylinder units 11, l2, with a pressure regulator 21. Likewise hydraulic circuits 22 interconnect the other pressure chambers of the piston and cylinder units with a second pressure regulator 24. The pressure regulators 2], 24 respectively receive hydraulic liquid under pressure by way of piping 25, 26 selectively from a changeover valve 27. When one of the regulators 21, 24 is receiving fluid under pressure the other regulator is automatically simultaneously set to provide exhaust passages. The hydraulic liquid under pressure in line 28' is applied by a conduit to the center chamber of the changeover valve 27.

The pressure regulators 21, 24 and the changeover valve 27 are operated together by a control piston 28 centrally positioned in a housing 29 containing the changeover valve. The control piston 28 is connected by axial arms 31, 32 to the pressure regulators 21, 24, and by radial anns 33, 34 to the operating piston of the changeover valve 27 and to a modifier cam 35 which also moves with the control piston 28. The positioning of the control piston 28 is determined by the admission of fluid selectively into end chambers 37, 38 disposed inside the housing 29 and connected through respective ducts 40, 41 to receive hydraulic liquid selectively from a vertically movable pilot valve 42 also mounted in the housing 29. When the control piston moves toward one of the pressure regulators, for example 21, the respective axial arm 31 will cause the regulator to open partially to increase the fluid pressure passed therethrough. Simultaneously, the other axial arm 32 will be withdrawn from its corresponding pressure regulator 24 to open a vent or exhaust port (not shown) in the latter regulator 24, for a purpose to be described more fully at a later point.

The position of the pilot valve 42 is controlled by a floating lever 43 having a fulcrum 44 disposed at the lower end of a slidable cam follower bar 45, which projects upwardly through a port in the housing 29 and engages, with its rounded upper end, a prearranged nonlinear profile of the modifier cam 35. A compression spring 47 holds the cam follower against the cam surface or profile. The other end of the floating lever 43 is connected by a link 49 to an arcuately movable arm 50 which is angularly positioned by a rate gyro 51 in accordance with the instantaneous roll velocity of the ship. The rate gyro 51 and arm 50 thus comprise a first member giving a first signal instantaneously representative of the roll velocity of the ship, while the pressure regulators 21, 24 and the operative parts of the housing 29 and lever 43 comprise a computer which positions the fin-tilting mechanism in accordance with the first signal as modified by the displacement of the cam follower 45. The cam follower displacement varies nonlinearly, as a consequence of the cam profile, with the setting of the regulators 21, 24 which control the torque applied to the fin. The axial displacement of the cam provides, therefore, a second signal varying linearly with torque and which is modified by the cam to provide a third signal representative of the cam follower displacement.

The pressure of fluid in the supply 28 is regulated by a pres-- sure regulator 60 whose setting is varied by a controller 61 which receives a signal indicative of the ships relative speed through the water.

The functioning of the control unit will now be explained by taking, for example, the case where the roll velocity of the ship causes the rate gyro arm 50 to move downwards in the drawing. This movement is transmitted through the link 49 to the lever 43 which rocks about the fulcrum 44 so that the piston of the pilot valve 42 moves upwardly. This connects the pressure supply 28 of fluid to the duct 41 extending to the chamber 38 on the right-hand side of the control piston 28 as shown in the drawing. This causes the control piston 28 to move to the left of the drawing. Pressure regulator 21 is thereby opened a predetermined amount while simultaneously opening exhaust passages (not shown) in the pressure regulator 24. The control piston movement is transmitted to the changeover valve 27 whose piston moves to the left allowing the pressure supply 28 to be applied to the pressure regulator 21. This allows hydraulic liquid to be fed through the hydraulic circuit to the left-hand working chambers of the piston and cylinder units ll, 12 at a predetermined pressure while simultaneously allowing hydraulic liquid to exhaust from their right hand working chambers by way of the hydraulic circuit 22 and the pressure regulator 24. The fins l, 2 are now tilted in respectively opposite directions by a torque which is directly proportional to the pressure at which fluid is admitted from the pressure regulator 21. This pressure is proportional to the position of the control piston 28 whose position is therefore represen tative of the tilting torque.

The movement of the control piston 28 also produces an axial displacement of the modifier cam 35. The axial position occupied by the cam 35 is therefore representative of the setting of the pressure regulator 21 due to the position of the control piston 28, and is therefore a measure of the torque applied to the fins. The instantaneous position of the cam 35 is transmitted, after modification by the cam profile, through the cam follower 45 to the fulcrum 44 of the lever 43. The posi tion of the pivot linking the link 49 to the lever 43 is a function solely of the movement of the arm 50 which is determined by the gyro, and therefore the downward movement of the cam follower 45 produces a downward movement of the piston of the pilot valve 42 about the pivotal connection of the link to the lever to a position which is a function of the profile of the cam 35 nd the tilting torque.

It will be appreciated that in this way the cam profile is able to correct for the change in center of pressure with the angle of attack of the fin. The function of the pressure regulator 60 is to provide a control for reducing the angle of attack of the fin for a given roll, with increased ships speed.

The gyro is a rate gyro which may be driven by fluid (as shown) or electrically to provide the signal proportional to the instantaneous velocity of roll. The profile of the cam 35 is so shaped that it provides the desired relationship between the tilting torque signified by the pressure at which hydraulic fluid is fed to the piston and cylinder units of the fin-tilting mechanisms, and the deflection of the rate gyro which is proportional to the instantaneous velocity of roll.

One advantage of the abovedescribed control unit is that it does not require a resetting signal from the fin.

Although the use of a centering spring to restore the fin to its midposition is primarily useful when a dynamically balanced fin is used, it should not be considered as being only useful for this purpose as there may be occasions when the combination of a centering spring and an unbalanced fin may offer decided advantages.

We claim:

1. A control unit supplying a signal to a ship-stabilizing fin. comprising a first member providing a first signal instantaneously representative of the roll velocity of the ship, a fin-tilting mechanism which varies the angle of attack of the fin through the water to stabilize the roll, connection means transmitting to the fin a torque-generating signal, a device connected to said connection means and providing a second signal representative of the torque applied to tilt the fin, a modifying element having a nonlinear characteristic compensating for the nonlinear relationship between the torque applied to the fin and its angle of attack, input means applying to the modify ing clement said second signal, output means deriving from the modifying element a third signal equivalent to the second signal after modification, and a computer controlling the fin tilting mechanism and determining the fin-tilt angle from said first and third signals.

2. A unit as set forth in claim 1, in which said computer comprises a floating lever, a rate gyro provides said first signal to rock the lever about its fulcrum, the third signal moves the fulcrum parallel to itself, and a pilot valve is positionally con trolled from the first and third signals applied to the lever and determines the setting of regulating means in said connection means.

3. A control unit for varying the tilt angle of a ship stabilizing fin, comprising a rate gyro providing a first signal representative of the roll velocity of the ship, a fluid pressure connection extending from a source of fluid under pressure to a fintilting mechanism, a first pressure regulator in said fluid pressure circuitry extending to one fin, a fluid pressure operated controller determining the setting of said regulator, pilot valve means controlling the setting of said controller, a first order floating lever positionally controlling said pilot valve means and having a fulcrum about which said lever is turned by said first signal, a cam having a nonlinear profile and moved in unison with said controller in accordance with a second signal the cam profile being shaped to compensate for the nonlinear relationship between the torque applied to the fin and its angle of attack, a cam follower riding on said cam and displacing said lever fulcrum parallel to itself and at right angles to said lever in accordance with a third signal provided by the cam modified second signal, and means controlling the pressure of the fluid supplied in accordance with the ships relative velocity.

4. A control unit as set forth in claim 3, in which two regulators are operated by said controller in opposite directions respectively to admit and discharge fluid pressure from piston sure supply valve positionally controlled with said cam by said piston, fluid pressure connections extending between working chambers at opposite ends of said piston and said pilot valve means, further connections extending from said fluid pressure supply valve to fluid pressure inlets of regulators associated with respective tin-tilting mechanisms, a fluid pressure inlet extending to said supply valve from a pressure regulator, and a controller adjusting the regulator in response to the ship's speed through the water. 

1. A control unit supplying a signal to a ship-stabilizing fin, comprising a first member providing a first signal instantaneously representative of the roll velocity of the ship, a fin-tilting mechanism which varies the angle of attack of the fin through the water to stabilize the roll, connection means transmitting to the fin a torque-generating signal, a device connected to said connection means and providing a second signal representative of the torque applied to tilt the fin, A modifying element having a nonlinear characteristic compensating for the nonlinear relationship between the torque applied to the fin and its angle of attack, input means applying to the modifying element said second signal, output means deriving from the modifying element a third signal equivalent to the second signal after modification, and a computer controlling the fin-tilting mechanism and determining the fin-tilt angle from said first and third signals.
 2. A unit as set forth in claim 1, in which said computer comprises a floating lever, a rate gyro provides said first signal to rock the lever about its fulcrum, the third signal moves the fulcrum parallel to itself, and a pilot valve is positionally controlled from the first and third signals applied to the lever and determines the setting of regulating means in said connection means.
 3. A control unit for varying the tilt angle of a ship stabilizing fin, comprising a rate gyro providing a first signal representative of the roll velocity of the ship, a fluid pressure connection extending from a source of fluid under pressure to a fin-tilting mechanism, a first pressure regulator in said fluid pressure circuitry extending to one fin, a fluid pressure operated controller determining the setting of said regulator, pilot valve means controlling the setting of said controller, a first order floating lever positionally controlling said pilot valve means and having a fulcrum about which said lever is turned by said first signal, a cam having a nonlinear profile and moved in unison with said controller in accordance with a second signal the cam profile being shaped to compensate for the nonlinear relationship between the torque applied to the fin and its angle of attack, a cam follower riding on said cam and displacing said lever fulcrum parallel to itself and at right angles to said lever in accordance with a third signal provided by the cam modified second signal, and means controlling the pressure of the fluid supplied in accordance with the ship''s relative velocity.
 4. A control unit as set forth in claim 3, in which two regulators are operated by said controller in opposite directions respectively to admit and discharge fluid pressure from piston and cylinder mechanisms applying tilting torque to respective fins.
 5. A unit as set forth in claim 4, in which the cam follower is spring biased against the cam and is displaced thereby at right angles to the cam displacement produced by said second signal.
 6. A control unit as set forth in claim 4, including a block containing pressure fluid compartments accommodating the cam, a piston forming the controller and having oppositely directed arms extending to respective regulators, a fluid pressure supply valve positionally controlled with said cam by said piston, fluid pressure connections extending between working chambers at opposite ends of said piston and said pilot valve means, further connections extending from said fluid pressure supply valve to fluid pressure inlets of regulators associated with respective fin-tilting mechanisms, a fluid pressure inlet extending to said supply valve from a pressure regulator, and a controller adjusting the regulator in response to the ship''s speed through the water. 